Occult Maxillary Sinus Phosphaturic Mesenchymal Tumor Localized by 68Ga-DOTATATE PET/CT After Repeated Negative Parathyroid Imaging.

We describe the imaging findings of a phosphaturic mesenchymal tumor arising in the left maxillary sinus in a 34-year-old woman with persistent hypophosphatemia and elevated parathyroid hormone levels who had undergone repeated evaluation for primary hyperparathyroidism despite negative parathyroid imaging. 68Ga-DOTATATE PET/CT demonstrated an unexpected somatostatin receptor-avid lesion in this exceptionally rare location. Surgical resection resulted in rapid biochemical and clinical recovery, while histopathology and single-cell RNA sequencing revealed a distinct FGF23- and PHEX-expressing tumor cell population, providing molecular confirmation of the imaging diagnosis.